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Study Of The Structure And Activity Mechanismabout FeO-SiO2 Slags

Posted on:2016-07-28Degree:MasterType:Thesis
Country:ChinaCandidate:B WangFull Text:PDF
GTID:2271330470962068Subject:Environmental Science and Engineering
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The emission of copper slag and nickel slag, two typical kinds of Fe O-Si O2 slags, are over 10 million tons per year. The slags have pozzolanic property and high content iron, however, low utilization and large accumulation lead to the waste of resource and environmental pollution. The purpose of this paper is to realize Fe O-Si O2 slags widely used in building materials based on the research about the structure and activity of the slags. Firstly physicochemical property, microscopic structure and leaching toxicity of slags were investigated. Then ions dissolution properties and pozzolanic property of slags were investigated. Next the chemically combined water content, active silica and active iron, and hydrated products after the pozzolanic reaction of slags with portlandite and dihydrate gypsum were investigated. Lastly the pozzolanic reaction mechanism of slags were inferred.The results showed that copper slag and nickel slag were acid slags, with the density of 3.8 g/cm3. And the main chemical components of slags were TFe and Si O2, reaching 70% of total weight, also contained a lot of heavy metal elements, such as Ni, Cr and Pb. The major mineral of the slags were fayalite and glass phase with high [Si O4] polymerization. The results of the leaching toxicity showed that the slags were general industrial wastes.The ions dissolution properties of TFe, soluble Si O2 and Al about copper slag and nickel slag were higher in the condition of p H < 2 and p H > 13, but close to zero in weak acid and alkali. The concentration of TFe and soluble Si O2 were 22.34mg/g and 10.17 mg/g of copper slag(CS16), 27.54mg/g and 12.25 mg/g of nickel slag(NS16), respectively, which ground 60 min and dissolved 6h in p H=2, while p H=13, the concentration were 0.62mg/g and 0.30 mg/g, 0.40mg/g and 0.47 mg/g, respectively. Furthermore the dissolution rate in strong acid was much higher than strong alkali, which caused by the dissolution of fayalite. The pozzolanic activity of the slags was very low in early hydration, which leaded to the strength of hydrated cement paste decline by adding into Portland cement, moreover the strength declined as the addition increase. But the activity gradually increased in the later hydration by the activation of portlandite generated by the hydration of Portland cement. The strength of paste approached to the contrast Portland cement and even surpassed, when addition 10% slags and hydration 28 d, and strength increasing with grind time prolonged. The main products of Portland cement contained the slags were hydrated calcium silicate and ettringite. A few hydrated calcium silicate had a high iron content, and the hydration reaction might be generate Fe(OH)2 gel.The pozzolanic activity was blast furnace slag > nickel slag > copper slag, and increasing with grind time prolonged. The increasing rules of chemically combined water and active Si O2 about blast furnace slag were fast in early but slow in later hydration, however, the rules about copper slag and nickel slag were opposite to blast furnace slag, and the contents in hydrated products were blast furnace slag > nickel slag > copper slag, by the reaction of slags with portlandite and dihydrate gypsum. However, the increasing rule of active Fe about copper slag and nickel slag were slow in early but fast in later hydration, while blast furnace slag had no obvious changes, and the content was nickel slag > copper slag > furnace slag. The content of chemically combined water of blast furnace slag, NS16 and CS16 were 12.09%, 4.13% and 2.42%, respectively, active Si O2 were 47.72mg/g, 20.96mg/g and 3.39mg/g, respectively, and active Fe were 0.23mg/g, 19.28mg/g and 7.9mg/g, respectively, after hydration 90 d with portlandite. The main hydrated products were C-S-H contained high proportion iron and Fe(OH)2 gel, adding dihydrate gypsum generated ettringite. Fayalite did not participate in the hydration reaction due to its stability with portlandite.The pozzolanic reaction mechanism speculation of Fe O-Si O2 slags is that the high [Si O4] polymerization in glass phase of the slag dissolves gradually, and generates [Si O4]4-, Fe2+ etc. ions in the OH- solution, and then reacts with Ca(OH)2 and H2 O, results in the generation of C-S-H and Fe(OH)2 gel. And some Fe2+ ions replace Ca2+ in the C-S-H structure which makes the Fe content in C-S-H increase.
Keywords/Search Tags:Copper slag, Nickel slag, Pozzolanic activity, High iron-containing hydration product, Hydration mechanism
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